1. Field of the Invention
The present invention relates to a process for forming in a silicon (Si) substrate a trench structure or deep-hole structure by dry etching. Particularly, the present invention relates to a technique which is useful when utilized in a field of manufacturing a product such as a Bi-CMOS semiconductor device having an isolation trench, a MOS capacitor device and so on that is made using Si material.
2. Related Arts
Conventionally, it is known to form a deep groove, i.e., trench, in a semiconductor device in order to perform insulation and isolation between elements. That is to say, each element formed on a silicon substrate is caused to be surrounded by a trench structure filled with a dielectric such as silicon dioxide (SiO.sub.2) or polysilicon surrounded with SiO.sub.2, thereby being isolated from other elements. Herein, trench etching performed is a technique for selectively etching in only the depthwise direction to thereby form a trench structure or deep-hole structure having a high aspect ratio. In order to form these structures in the manufacturing process, it is required that the etch selectivity against a silicon dioxide (SiO.sub.2) film which is a masking material be high, that the etch rate be uniform, and that the anisotropy of the etch be high.
As the above-mentioned trench etching technique there is known a dry etching technique which is described in Japanese Patent Application Laid-open No. HEI-6-163478. The dry etching technique described therein uses as an etching gas a mixed gas of bromine-containing gas (hereinafter referred to as "Br system gas"), oxygen-containing gas (hereinafter referred to as "O.sub.2 system gas"), silicon tetrafluoride (SiF.sub.4), and sulfur hexafluoride (SF.sub.6) or nitrogen trifluoride (NF.sub.3).
However, in the above-mentioned dry etching technique, there is the problem that the etch rate is low although the requirements of high anisotropy and high etch selectivity against SiO.sub.2 mask are satisfied.